DISSECTING KNIVES, ETC. 



73 



The mode adopted for breaking up tissues into very small pieces is 

 usually conducted as represented at fig. 56, with a pair of the small 



fig. 54. 



needles held firmly between the fore-finger and thumb. The structure 

 must be teased out ; an operation which requires care and perseverance, 



fig. 55. 



as most of the animal tissues are very difficult of separation, especially 

 when it is wished to examine them under high powers. All substances 



fig. 56. 



should be carefully separated from dust and other impurities which 

 would render their structure indistinct, or confusing. With very deli- 

 cate membranes, and with those of the nervous system of the smaller 

 animals, insects, &c.,-it becomes necessary that the investigation should 



